Air swept rotary beater and separator with oversize-material return tube means to the air inlet



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2,552,565 sEPARAToR WITH ovERsIzE-MATERIAL May 15, 1951 J. F. Les vEAux AIR SWEPT ROTARY BEATER AND RETURN TUBE MEANS To THE Arx INLET '2 Sheets-Sheet 2 Filed June 26, 1947 Patented Niay 15, 1951 UNITED STATES PATENT OFFICE John F. Les Veaux, Middleport, N. Y., assignor to Food Machinery and Chemical Corporation, a

corporation of Delaware Application June 26, 1947, Serial No. '757,117

1 Claim. 1 The invention relates t0 improvements in pulverizing mills, and more particularly to improve- `ments in mills of the pulverizing and classifying type disclosed in Patent No. 2,362,142, granted to H. G. Lykken et al., November '7, 1944. The general operation of the present device is similar to Iwhat is set forth in the above patent. Some defects have been found to be present in the operation of the machine disclosed in said patent, and the primary object of the present invention is accordingly to overcome such shortcomings and diiculties as have become apparent during the course of commercial operation.

In mills of this type, in which classification of the pulverized material is accomplished by drawing air through a forced Vortex, ne material is drawn to the center of the vortex and discharged through an annular space at the top of the vortex. Coarse, unground material remains in the vortex and tends to accumulate there, which accumulation detracts from the grinding operae tion and reduces the flow of ground material through the mill, thereby reducing the capacity Of the mill.

In order to overcome these diiculties the present invention contemplates the use of a tubular connection extending from the inner surface oi the grinding chamber near the discharge end thereof t0 the air inlet of the grinding chamber.

Since coarse particles will be drawn against the y inside oi the grinding chamber' they will be discharged from the chamber and passed through said tubular connection to the inlet of the mill for further grinding. The size oi the tube is just suiiicient to discharge the coarse particles, which are largely thrown out by centrifugal force, `and should not be large enough to draw an appreciable amount of air out of the grinding chamber, since this would tend to reverse the flow of iine material to the outside instead of to the inside of the vortex and would thereby discharge the fine material through the return tube instead of through the discharge outlet of the mill. Accordingly, the amount of air drawn off with the coarse material through the tube and recirculated to the air inlet of the mill comprises only a small percentage of the total air passing through the mill.

I am aware that fans have been employed for the purpose of exhausting dust-laden air and for collecting the dust by discharging the dust through a small opening in the periphery of the ian casing while the major portion of the air is discharged from a normal fan outlet so that the dust is collected and relatively pure air is discharged, but no construction is known to me in which a return tube is employed in the arrangement set forth in the present disclosure.

The invention will be more readily understood by reference to the accompanying drawing and the following detailed description, in which are set forth by way of illustration certain specific embodiments of the inventive thought.

In the drawings:

Fig. 1 is a vertical sectional View of a grinding mill with parts shown in operation, the section being taken on line I--I of Fig. 3;

Fig. 2 is a vertical section through the grinding mill taken at right angles to the section shown in Fig. 1, parts being shown in elevation, the section being taken on line 2-2 of Fig. 3;

Fig. 3 is a horizontal section on the line 3 3 of Fig. 2; and

Fig. 4 is a diagrammatic section with parts omitted showing a modification in which the grinding chamber is oi conical rather than cylindrical form.

As sho-wn the mechanism constituting the grinding mill is mounted upon a suitable base It which supports a cylindrical housing or casing II for the grinding mechanism, and at a point suitably spaced therefrom is mounted a motor I2 which serves to actuate the grinding mechanism of the mill. A small motor I 3 designed to actuate the feed screw for introducing the material to be ground into the mill is shown as mounted upon a bracket lf3 extending laterally from the base.

At the top of the cylindrical casing II is mounted a fan casing I5. A main drive shaft I6 is centrally mounted with reference to the mill casing II and ian casing i5 and is provided with suitable upper and lower bearings Il and I8 located at the top of the fan casing and on the base lli, respectively. The main shaft I6 is adapted to be driven from the motor I2 by any suitable means, as, for example, V-belts I9 and pulleys 2) and 2l carried by the motor shaft and main driving shaft respectively.

A grinding chamber 22 is provided within the cylindrical casing I! and has a downwardly in I' clined bottom portion Z3 carried by the casing II and having a central airinlet opening 24 formed therein surrounding the drive shaft I 6. An air chamber 25 is provided below the inclined bottom member 23 having a lateral passage or intake box 26, herein shown as rectangular in cross section. The grinding chamber 21E is pro" vided with a hardened liner 2l iitting within the outer casing I I. At the top of the chamber there is provided a plate 28 lwhich divides the grinding chamber from the fan chamber included within material.

the casing I5. The plate 28 is provided with a central opening 29 to permit communication between the grinding chamber and the fan chamber, this opening being formed concentric with the drive shaft I6.

A pulverizing .rotor is mounted within the grinding vchamber 22 and comprises a plurality of radial blades 3S, herein shown as mounted upon a hub 3| secured to the driving shaft I6. A plurality of disks 32 of less diameter than the rotor itself are secured to the blades and welded to the hub 3l. These disks are Vto reinforce the blades. A bottom disk 33 of greater diameter than the disks 32 and extending to the periphery of the radial blades is secured to the bottoms of such blades and is spaced slightly from the inclined bottom 23 of the grinding chamber to allow air to enter the grinding chamber from the inlet 24 through a peripheral space 34.

The fan casing 'I5 encloses a fan chamber f 35 within which is mounted a fan runner cornprising a ring 3S secured to a hub 3l mounted on the drive shaft V5 and equipped with radial blades 3B. The fan casing may be provided with a discharge outlet @il similar to that shown in Fig-.l3 of Patent No. 2,362,142.

rlhe material to be treated is supplied to the grinding chamber by means of a feed screw iii mounted in a housing di communicating through an opening `in the chamber wall interior oi the grinding chamber. The housing lll is suitably Secured to the cylindrical wall l l of the grinding chamber.

The feed kscrew 'Z0 may be driven through any suitable means, as, vfor example, a variable'speed drive l2 from the motor i3. A feed hopper i3 supplies the material to the feed screw ll.

The above described mechanism may be of know-n construction .and as shown is similar in many respects to what is disclosed in Patent No. 2,362,142, although it will be obvious that the invention is not limited to such details of vconstruction.

In accordance with the present invention a recirculation tube .is provided connecting the interior of the grinding chamber 22 with the top ofthe inlet box 26. To accommodate such tube an oval shaped opening 5l is provided in the upper portion of the casing wall ll and the liner 23, and an opening `52 is provided in the top of the lateral inlet box 26.

The axis of the tube 56 is substantially Vtangential to the cylindrical casingV H and at its other end the tube joins the intake box at an acute angle in the direction of air ilow.

The operation of the device is as follows: The motor l2 drives the main shaft I6 and radial blades 3@ at a high rate of speed. The fan runner within the casing i5' also revolves at a high rate of speed and draws air through the inlet box 25 and the inlet 24 into the grinding chamber 22, from which it is passed out through the discharge opening 2Q into the fan chamber within the casing 5'5. The discharge outlet '6G from the fan may be connected to a suitable dust collector (not shown) for recovery of the ground The Vmaterial to be ground is placed in the hopper 43 and fed through the walls l l and 21 of the grinding chamber 22 by means or" the feed screw lill. The rapidly rotating blades 30 of the rotor pulverize the material and create a forced. vortex so that the material is drawn by centrifugal force against the inner wall of the grinding chamber and is rapidly whirled around. The material which has been suflicientlypulver- 4 ized and is-therefore capable of being drawn radially inward against centrifugal force is discharged through the opening 29 into the fan housing l5 and is thence discharged through the Yopening iii into the dust collector (not shown). If the mill is operated at high capacity too great a quantity of coarse particles may accumulate within the grinding chamber, and this condition tends to prevent the flow of finely pulverized Vparticles through the mill unless means are provided for progressing the coarse particles longitudinally through the cylinder. According to the preferred embodiment of my invention the tube 50 is provided for this purpose. The coarse particles which are whirling around against the Vinner `wall of the grinding chamber 22 are discharged by centrifugal force together with a certain amount of air blast into the tube 5E! and they particles are returned with the inlet air through the intake box 26 into the chamber 22 for further grinding. This arrangement insures a defini-te flow of dust upwardly through the mill and allows the iinely ground particles t0 be discharged, thus increasing the capacity of the mill and improving the classication. All material ithin the mill tends to be drawn upwardly through the mill, which results in a mixture of coarse and fine material at the top of the mill. By returning the coarse material to the bottom ofthe mill it will pass through a region relatively free of fine material where there is less cushioning effect from the finer material. Greater attrition and faster grinding result, which also increases the mill capacity.

A modification of the invention is shown in Fig. 4, in which the parts may be similar to what has been set forth in the previously described embodiment except that the wall Ha of the grinding chamber is frusto-conical in form, being Vinclined inwardly and upwardly from the base, and the radial blades 38e are similarly inclined in order to nt within the grinding chamber. This conical larrangement of the walls tends to force the coarse material downwardly and retain such material in the lower part of the mill, where it can be more effectively ground since the ne material will be drawn by the air to the upper part Vof the mill and discharged from the outlet 'of the fan casing. A return pipe 5l]a similar to the pipe 5E in the previously described embodiment of the invention may be employed if desired in connection with the conical walled grinding chamber, although this return pipe is of less importance in the case of a conical walled #chamber than in the case of a chamber having cylindrical walls.

Further `modiiicatio'ns and variations in detail may be resorted to without departing from the spirit of the invention, Vas will be apparent to those skilled in the art.

I claim:

In van .attrition grinding mill, an upright chamber having walls of circular cross section, a pulverizing rotor concentrically mounted in the grinding chamber, said chamber having aligned laxial air inlet and outlet openings at the bottom and top thereof respectively, an air intake chamber located below 'the air intake opening Vand having Va laterally lextending intake passage communicating therewith, means for supplying material to be ground to the grinding chamber and communicating with said chamber through a lateral opening intermediate the ends thereof, means for .actuating said grinding rotor at a high rate of speed/.for grinding said material, means for moving air axially through the mill comprising a fan located above the grinding chamber and com muncating therewith through the grinding chamber outlet opening, and a conduit leading from a hole in the peripheral wall of the chamber near the upper end thereof to the laterally extending intake passage, whereby coarse particles are withdrawn from the inside of the chamber and are passed to the inlet of the chamber for regrinding. l0

JOHN F'. LES VEAUX.

REFERENCES CITED The following references are of record in the x5 le of this patent:

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